The present invention relates to a droplet deposition apparatus including an actuator, and to a control circuit for an actuator.
Ink jet printers include an ink actuator for ejecting droplets of ink liquid on demand. Such an ink actuator is disclosed in U.S. Pat. No. 5,016,028. The actuator includes a plurality of channels having side walls which are displaceable in response to electric drive signals. When an electric drive signal is applied to a section of the wall, the wall will move, thereby causing the volume of corresponding channels to increase or decrease.
U.S. Pat. No. 5,631,675 describes an apparatus for driving piezoelectric units of an ink jet recording head. The apparatus according to U.S. Pat. No. 5,631,675 includes two constant current sources which operate to charge and discharge a capacitor. The voltage of the capacitor is amplified to provide the voltage for driving the piezoelectric units.
EP 0 778 132 discloses a head driving device including an ink jet head having a number of ink chambers arranged side by side and separated by piezo-electric elements and Field effect Transistors for connecting electrodes of the ink chambers to a +VCC power source line, and to a xe2x88x92VCC power source line, respectively, and bi-directionakl switches for connecting the electrodes to a ground line.
A problem to which the present invention is directed is to improve print performance and to further increase the yield in the manufacture of droplet deposition apparatuses.
This problem is addressed by a droplet deposition apparatus comprising an actuator having a plurality of spaced piezoelectric walls defining channels, said walls having opposed sides; said opposed sides being provided with electrodes being adapted to receive electric signals to deform said walls to cause liquid in said channels to be ejected therefrom; said signals having wave-forms; and a control unit comprising means for providing an individually adapted signal slope of the wave form to selected electrodes. Moreover, the signal slope control means includes a plurality of current signal sources having at least two individually activatable current sources for one actuator channel so as to enable provision of an individually adapted signal slope of the wave form to a selected electrode; and the control unit comprises a power supply input for receiving a controlled voltage level.
This solution makes it possible to obtain at least two different slopes of the output signal so as to compensate for individual channel deviations.
The signal slope control means may include means for setting compensation data so as to adapt the signal slope of the wave form for an individual channel deviation. In this manner each channel of an actuator may be adjusted and set to a selected liquid droplet ejection speed.
According to a preferred embodiment the droplet deposition apparatus includes means for setting a selected uniform droplet velocity of ejected droplets. This may be achieved by adjusting a maximum drive voltage level to a selected value, and by setting a maximum drive current for each channel so as to obtain a selected droplet velocity for each channel. In this manner there is ensured a uniform response to print orders and the deviation between different droplet deposition apparatuses as well as the deviation between channels is minimized or eliminated.